1. Field of the Invention
The present invention relates to injection molding machines and, more particularly, to a supporting structure for a granulate hopper on the injection unit of an injection molding machine which offers the possibility of shifting the granulate hopper laterally away from the charge chute of the injection unit.
2. Description of the Prior Art
A typical injection unit has two parallel guide rods supporting a carrier bridge with a central plastification cylinder and cooperating plastification screw. The carrier bridge also supports a raw material hopper containing the granular plastic raw material for the injection molding machine.
The hopper typically has a conical bottom portion from which the granulate is fed downwardly into the plastification cylinder through a charge chute. Such a hopper supporting structure is disclosed in German Auslegesschrift (Publ. Allowed Application) No. 28 47 980 and in German Offenlegungsschrift (Publ. Application) No. 29 20 584. Major portions of both applications are also contained in U.S. Pat. No. 4,251,204. These publications suggest granulate hoppers of small to medium capacity.
Typically, the hopper is made of steel sheet, having a conical lower hopper section, to the outlet extremity of which is attached an annular reinforcing collar. The latter has a generally triangular cross section defined by a cylindrical outer surface and a hopper-supporting conical inner surface. To the reinforcing collar is bolted a tubular connector which, in turn, is releasably clampable to a tubular extension of the carrier bridge of the injection unit. In situations, where the injection unit is so arranged that its charge chute is oriented horizontally, an intermediate connecting cylinder may be utilized, in which case the hopper is mounted vertically on the horizontal connecting cylinder. The above-mentioned Offenlegungsschrift also suggests a hopper mounting structure which includes a transversely oriented guide plate at the entrance to the charge chute of the injection unit and a cooperating dovetailing groove in the reinforcing collar of the granulate hopper. This configuration makes it possible to shift the hopper laterally away from the charge chute of the injection unit and into alignment with a discharge bore in the guide plate, so that the hopper can be emptied of its granulate contents.
These prior art hopper supporting structures have certain disadvantages, especially in connection with hoppers of large capacity, or in connection with hoppers which, for one or the other reason, may be oriented at an inclination or may have an asymmetrical outline. The requirement of having absolutely smooth continuous surfaces inside the conical lower hopper section puts certain limitations on the hopper supporting structure, especially on the connection between the outlet extremity of the hopper and the annular reinforcing ring. It has been found that an inclined or asymmetrical hopper may create fatigue failure in the prior art hopper mounting structure.